A human gut symbiont degrades complex plant carbohydrates.

What is it about?

Xyloglucan is a complex polysaccharide found in the majority of plant material in the human diet. However, it's digestion in our gut is performed entirely by symbiotic bacteria, as we lack the necessary enzymes to deconstruct it. In this study, we demonstrated that one gut species in particular, Bacteroides ovatus, can degrade xyloglucan completely into single metabolisable sugars. We were able to show that this ability is conferred by one genetic operon, and could study how this operon has evolved in the gut bacterial lineage. Knocking out this operon, or parts of it, meant that the bacterium was no longer able to grow on xyloglucan. We could also verify using mouse models that xyloglucan in the diet favours B.ovatus in the gut community.

Why is it important?

This was the first complete characterisation of this type of carbohydrate-degrading locus, and a very convincing demonstration of the link between genetics and carbohydrate metabolism in this manner. Our observations relate to the study of human diet, nutrition, and health, and may inform strategies to manipulate the gut microbiota to improve digestion.

Perspectives

Dr Lauren S McKee

Kungliga Tekniska Hogskolan

This first complete PUL characterisation, where biochemistry, structural biology, and bacterial genetics were combined to study one locus, opened up the field to a wider community of researchers. This is now a central core of the field of carbohydrate active enzyme investigation, and is beginning to intersect with broader studies of the microbiome and its role in host health.